The role of viruses as possible teratogens is under investigation. The wild strain of Reo I virus causes fetal death as well as severe hydrocephalus when inoculated into rhesus monkey fetuses. Control animals were not affected. We have established that the patas monkey Erythrocebus patas is susceptible to oral infections of Toxoplasma gondii. The infection becomes persistent and the organism can be isolated from monkey lymph nodes several months after oral intubation of Toxoplasma gondii cysts.